This application is in response to RFA-87-AI-CA-03. The focus of this application is to obtain information relating to the structure and function of the HIV env gene product and its cellular receptor, the T4 protein, which can provide the basis of the design of drugs capable of interfering with the interaction between these components, and which thus can block infection by HIV. The majority of the investigators participating in this program are at SUNY-Buffalo, with additional projects to be carried out at the Buffalo Medical Foundation, the University of Rochester, and Roswell Park Memorial Institute. None of the investigators involve are retrovirologists, and the proposed projects do not entail studies of either HIV or HIV-infected cells. The key to this program is the recent preparation by Dr. Rekosh of an SV40 vector which efficiently expresses the cloned HIV env gene.